Display device and manufacturing method thereof

ABSTRACT

A manufacturing method of a display device includes: forming a flexible substrate on a sacrificial substrate; forming a display element unit on a first surface of the flexible substrate, the display element unit including a TFT and an organic light-emitting element; separating the sacrificial substrate from the flexible substrate; and forming a protective layer by depositing an organic material on a second surface of the flexible substrate, the second surface being opposite to the first surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/455,037, filed on Mar. 9, 2017, and claims priority from and thebenefit of Korean Patent Application No. 10-2016-0114434, filed on Sep.6, 2016, which are hereby incorporated by reference for all purposes asif fully set forth herein.

BACKGROUND Field

Exemplary embodiments relate to a display device and a manufacturingmethod thereof.

Discussion of the Background

There are various display devices such as a liquid crystal display(LCD), an organic light-emitting display, and the like.

The organic light-emitting display, unlike the LCD, does not need abacklight unit, and thus, the thickness of the organic light-emittingdisplay can be minimized. Accordingly, studies have been conducted on aflexible, stretchable, foldable, bendable, or rollable organiclight-emitting display.

However, as the thickness of a display device decreases, the impactresistance of the display device may weaken, and for this reason, aprotective film may be formed below a display element unit of thedisplay device. However, UV irradiation or thermal treatment that may beperformed during the formation of the protective film may cause damageto elements of the display device.

If the amount of UV light or heat applied to form the protective film isminimized to prevent damage to the elements of the display device, thethickness of the protective film may not be able to be properlyincreased.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the inventive concept,and, therefore, it may contain information that does not form the priorart that is already known in this country to a person of ordinary skillin the art.

SUMMARY

Exemplary embodiments provide a display device including a protectivelayer, which is for protecting the display device against physicalimpact and preventing moisture or foreign materials from infiltratinginto the display device, and a manufacturing method of the displaydevice.

Exemplary embodiments also provide a display device including aprotective layer, which is formed by depositing an organic material atlow temperature without irradiation so as to prevent elements in thedisplay device from being damaged by light or heat, and a manufacturingmethod of the display device.

Additional aspects will be set forth in the detailed description whichfollows, and, in part, will be apparent from the disclosure, or may belearned by practice of the inventive concept.

Exemplary embodiments provide a display device including: a flexiblesubstrate; a display element unit disposed on a first surface of theflexible substrate and including a thin-film transistor (TFT) and anorganic light-emitting element coupled to the TFT; and a protectivelayer including an organic material and disposed directly on a secondsurface of the flexible substrate, the second surface being opposite tothe first surface.

Exemplary embodiments provide a display device including: a displayelement unit including a TFT and an organic light-emitting elementcoupled to the TFT; and a protective layer disposed on a first surfaceof the display element unit and comprising at least one material ofFormula 1:

where n is a natural number equal to or greater than 2, m is an integernumber between 0 and 4, X is hydrogen or halogen, and R is halogen oralkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl,or a halide thereof having 1 to 8 carbon atoms.

Exemplary embodiments provides a manufacturing method of a displaydevice, comprising: forming a flexible substrate on a sacrificialsubstrate; forming a display element unit, including a TFT and anorganic light-emitting element, on a first surface of the flexiblesubstrate; separating the sacrificial substrate from the flexiblesubstrate; and forming a protective layer by depositing an organicmaterial on a second surface of the flexible substrate, the secondsurface being opposite to the first surface.

According to exemplary embodiments, a display device can be protectedagainst physical impact, and can be prevented from being damaged bymoisture or foreign materials infiltrating thereto.

In addition, since the protective layer may be formed by depositing anorganic material at low temperature without irradiation, elements in thedisplay device can be prevented from being damaged by light or heat.

The foregoing general description and the following detailed descriptionare exemplary and explanatory and are intended to provide furtherexplanation of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the inventive concept, and are incorporated in andconstitute a part of this specification, illustrate exemplaryembodiments of the inventive concept, and, together with thedescription, serve to explain principles of the inventive concept.

FIG. 1 is a cross-sectional view illustrating a stack structure of adisplay device according to an exemplary embodiment.

FIG. 2 is an enlarged cross-sectional view of a part A of the displaydevice of FIG. 1.

FIG. 3 is a cross-sectional view illustrating an arbitrary multilayerstack bent by external stress.

FIG. 4 is a cross-sectional view illustrating neutral planes of displaydevices.

FIG. 5 is a cross-sectional view illustrating a stack structure of adisplay device according to another exemplary embodiment.

FIG. 6, FIG. 7, and FIG. 8 are cross-sectional views illustrating stackstructures of display devices according to other exemplary embodiments.

FIG. 9, FIG. 10, and FIG. 11 are cross-sectional views illustratingstack structures of display devices according to still other exemplaryembodiments.

FIG. 12, FIG. 13, FIG. 14, FIG. 15, and FIG. 16 cross-sectional viewsillustrating a manufacturing method of a display device, according to anexemplary embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of various exemplary embodiments. It is apparent, however,that various exemplary embodiments may be practiced without thesespecific details or with one or more equivalent arrangements. In otherinstances, well-known structures and devices are shown in block diagramform in order to avoid unnecessarily obscuring various exemplaryembodiments.

In the accompanying figures, the size and relative sizes of layers,films, panels, regions, etc., may be exaggerated for clarity anddescriptive purposes. Also, like reference numerals denote likeelements.

When an element or layer is referred to as being “on,” “connected to,”or “coupled to” another element or layer, it may be directly on,connected to, or coupled to the other element or layer or interveningelements or layers may be present. When, however, an element or layer isreferred to as being “directly on,” “directly connected to,” or“directly coupled to” another element or layer, there are no interveningelements or layers present. For the purposes of this disclosure, “atleast one of X, Y, and Z” and “at least one selected from the groupconsisting of X, Y, and Z” may be construed as X only, Y only, Z only,or any combination of two or more of X, Y, and Z, such as, for instance,XYZ, XYY, YZ, and ZZ. Like numbers refer to like elements throughout. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

Although the terms first, second, etc. may be used herein to describevarious elements, components, regions, layers, and/or sections, theseelements, components, regions, layers, and/or sections should not belimited by these terms. These terms are used to distinguish one element,component, region, layer, and/or section from another element,component, region, layer, and/or section. Thus, a first element,component, region, layer, and/or section discussed below could be termeda second element, component, region, layer, and/or section withoutdeparting from the teachings of the present disclosure.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for descriptive purposes, and,thereby, to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the drawings. Spatiallyrelative terms are intended to encompass different orientations of anapparatus in use, operation, and/or manufacture in addition to theorientation depicted in the drawings. For example, if the apparatus inthe drawings is turned over, elements described as “below” or “beneath”other elements or features would then be oriented “above” the otherelements or features. Thus, the exemplary term “below” can encompassboth an orientation of above and below. Furthermore, the apparatus maybe otherwise oriented (e.g., rotated 90 degrees or at otherorientations), and, as such, the spatially relative descriptors usedherein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. As used herein, thesingular forms, “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Moreover,the terms “comprises,” “comprising,” “includes,” and/or “including,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, components, and/orgroups thereof, but do not preclude the presence or addition of one ormore other features, integers, steps, operations, elements, components,and/or groups thereof.

Various exemplary embodiments are described herein with reference tosectional illustrations that are schematic illustrations of idealizedexemplary embodiments and/or intermediate structures. As such,variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, exemplary embodiments disclosed herein should not beconstrued as limited to the particular illustrated shapes of regions,but are to include deviations in shapes that result from, for instance,manufacturing. Accordingly, the regions illustrated in the drawings areschematic in nature and their shapes are not intended to illustrate theactual shape of a region of a device and are not intended to belimiting.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure is a part. Terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and will not be interpreted in anidealized or overly formal sense, unless expressly so defined herein.

Display devices according to exemplary embodiments may be self-emissivedisplay devices such as organic light-emitting displays or plasmadisplay devices, or may be light-receiving display devices such asliquid crystal display (LCDs) or electrophoretic displays (EPDs).Display devices according to exemplary embodiments will hereinafter bedescribed with respect to a flexible organic light-emitting displaydevice as an example, but the exemplary embodiments are not limitedthereto.

FIG. 1 is a cross-sectional view illustrating a stack structure of adisplay device 1 according to an exemplary embodiment.

Referring to FIG. 1, a display device 1 includes a protective layer 10,a flexible substrate 20, which is disposed on the protective layer 10,and a display element unit 100, which is disposed on the flexiblesubstrate 20.

The display device 1 may include a plurality of pixels, which arearranged in any suitable formation, such as a matrix formation over aplane. The display element unit 100 of the display device 1 may includea driving element, which drives each of the pixels. The driving elementsinclude signal transmission elements such as a gate line, a data line,and a thin-film transistor (TFT) and a light-emitting element such as anorganic light-emitting layer.

At least one of a first surface (e.g. a top surface) and a secondsurface (e.g. a bottom surface) of the display element unit 100 may bedisplay surfaces of the display device 1.

The flexible substrate 20, which is disposed on the second surface ofthe display element unit 100, not only supports the display element unit100, but also provides flexibility to the display device 1 such that thedisplay device 1 may be bendable, foldable, or rollable. The flexiblesubstrate 20 may include a first surface contacting the display elementunit 100 and a second surface opposite to the first surface.

The protective layer 10, which is disposed on the second surface of theflexible substrate 20, not only prevents moisture or foreign materialsfrom infiltrating into the flexible substrate 20 or the display elementunit 100, but also protects the display element unit 100 againstphysical impact. The protective layer 10 may be disposed directly on thesecond surface of the flexible substrate 20 without any adhesive layerinterposed therebetween.

In exemplary embodiments, the display device 1 may further include aprotective film 220, which is disposed on the first surface of thedisplay element unit 100. The protective film 220, like the protectivelayer 10, may protect the display element unit 100 against moisture orforeign materials. The protective film 220, unlike the protective layer10, may be disposed on the display element unit 100 with an adhesivelayer 210 interposed therebetween.

A cross-sectional structure of the display device 1 will hereinafter bedescribed in further detail with reference to FIG. 2.

FIG. 2 is an enlarged cross-sectional view of a part A of the displaydevice 1 of FIG. 1.

Referring to FIG. 2, the protective layer 10 is disposed at a lowermostpart of the display device 1. The protective layer 10 protects thedisplay device 1 against foreign materials or physical impact and maylower a neutral plane of the display device 1.

The combined thickness of the protective layer 10 and the flexiblesubstrate 20 may be set to be 20 μm or thicker. In a case where thecombined thickness of the protective layer 10 and the flexible substrate20 is 20 μm or thicker, the neutral plane may be lowered such that mosttensile force may act on the protective layer 10 and the flexiblesubstrate 20, and thus, the display element unit 100 may be protectedagainst the tensile force. For example, the neutral plane may beextended along at least one of the protective layer 10 and the flexiblesubstrate 20. The lowering of the neutral plane may depend on thecombined thickness of the protective layer 10 and the flexible substrate20. Thus, even if the thickness of the flexible substrate 20 is lessthan 20 μm, the insufficient thickness of the flexible substrate 20 maybe compensated for by the protective layer 10, and thus, the neutralplane may be effectively lowered. As a result, flexible substrates ofvarious thicknesses may be selected for the display device 1. Thelowering of the neural plane will be described later in further detail.

The protective layer 10 may include an organic material. The protectivelayer 10 may be formed by depositing the organic material. That is, theprotective layer 10 may include an organic deposition layer. Since theprotective layer 10 may be formed by depositing the organic material onthe second surface of the flexible substrate 20, the protective layer 10may be disposed to directly contact the second surface of the flexiblesubstrate 20 without any adhesive layer interposed therebetween. Byforming the protective layer 10 directly on the second surface of theflexible substrate 20, the thickness of the display device 1 may bereduced, and the neutral plane may be effectively lowered.

The organic material of the protective layer 10 may be a material thatcan be deposited at a low temperature of, for example, 90° C. or lower.

For example, the organic material of the protective layer 10 may includeat least one of parylene (i.e., a poly(p-xylylene) polymer) and aderivative thereof, which may be represented by Formula 1:

where n is a natural number equal to or greater than 2, m is an integernumber between 0 and 4, X is hydrogen or halogen, and R is halogen oralkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl,or a halide thereof having 1 to 8 carbon atoms.

The material represented by Formula 1 may include at least one ofmaterials represented by Formulas 2 through 5:

where n is a natural number equal to or greater than 2.

The protective layer 10 may have a Young's modulus of 20 GPa or lower.In this case, the protective layer 10 may protect the display device 1without reducing the overall flexibility of the display device 1.

The Young's modulus of the protective layer 10 may be lower than, orsimilar to, the Young's modulus of the flexible substrate 20. In thiscase, the protective layer 10 may protect the display device 1 withoutadversely affecting the flexibility or the curvature of the displaydevice 1.

The protective layer 10 may have a water vapor transmission rate (WVTR)of 10⁻³ g·mm/m²/day or less. In this case, moisture in the outside airmay be effectively prevented from infiltrating into the display elementunit 100 of the display device 1. Thus, the provision of any additionalwaterproof member in the display device 1 may be unnecessary.

The protective layer 10 may have a coefficient of thermal expansion(CTE) of 15×10⁻⁶/K or lower. In this case, the protective layer 10 maybe prevented from being peeled off from the display device 1 byrepeating thermal expansion and contraction.

The bottom of the protective layer 10 may be hard-coated by UVirradiation or thermal treatment. As mentioned above, if the protectivelayer 10 has a CTE of 15×10⁻⁶/K or lower, the protective layer 10 may beprevented from being peeled off from the display device 1 during a hardcoating process using thermal treatment.

The flexible substrate 20 is disposed on the protective layer 10. Theflexible substrate 20 may be flexible enough to allow the display device1 to maintain its display performance even in a bent state. The flexiblesubstrate 20 may be formed to have a thin thickness and may include amaterial such as flexible glass having elasticity.

For example, the flexible substrate 20 may include polyimide (PI), butthe exemplary embodiments are not limited thereto, the flexiblesubstrate 20 may include flexible glass.

The display element unit 100 is disposed on the flexible substrate 20.The display element unit 100 may include a buffer layer 110, an activelayer 121, a gate insulating layer 140, a gate electrode 151, aninterlayer dielectric layer 160, a source electrode 172, a drainelectrode 173, a passivation layer 180, an organic light-emittingelement E, and an encapsulation layer 194.

The buffer layer 110 is disposed at a lowermost part of the displayelement unit 100. The buffer layer 110 may be disposed on the flexiblesubstrate 20. The buffer layer 110 may include silicon nitride(SiN_(x)), silicon oxide (SiO_(x)), or silicon oxynitride (SiO_(x)N_(y))and may be formed as a single layer or a multilayer. The buffer layer110 prevents the infiltration of impurities, moisture, or the outsideair that may degrade semiconductor characteristics, and may planarizethe surface of the flexible substrate 20.

The active layer 121 is disposed on the buffer layer 110. The activelayer 121 may include a semiconductor and may be formed of polysilicon.

The active layer 121 may include a channel region 123 and source anddrain regions 122 and 124, which are disposed on both sides of thechannel region 123. The channel region 123 may be an intrinsicsemiconductor such as polysilicon not doped with impurities, and thesource and drain regions 122 and 124 may be impurity semiconductors suchas polysilicon doped with conductive impurities.

The gate insulating layer 140 is disposed on the active layer 121. Thegate insulating layer 140 may include an insulating layer having siliconnitride, silicon oxide, or silicon oxynitride and may be formed as asingle layer or a multilayer.

The gate electrode 151 is disposed on the gate insulating layer 140 andoverlaps the channel region 123 of the active layer 121. The gateelectrode 151 may be connected to a gate line (not illustrated) and agate pad (not illustrated). The gate electrode 151 may include aluminum(Al), molybdenum (Mo), copper (Cu), or an alloy thereof and may have amultilayer structure.

The interlayer dielectric layer 160 is disposed on the gate electrode151. The interlayer dielectric layer 160 may include an insulating layerhaving silicon nitride, silicon oxide, or silicon oxynitride and may beformed as a single layer or a multilayer.

The source and drain electrodes 172 and 173 are disposed on theinterlayer dielectric layer 160. The source electrode 172 may beconnected to the source region 122 of the active layer 121 via a sourcehole 161 formed in the gate insulating layer 140 and the interlayerdielectric layer 160, and the drain electrode 173 may be connected tothe drain region 124 of the active layer 121 via a drain hole 162 formedin the gate insulating layer 140 and the interlayer dielectric layer160. The source electrode 172 may be connected to a data line (notillustrated) and a data pad (not illustrated).

Each of the source and drain electrodes 172 and 173 may include Al, Mo,chromium (Cr), tantalum (Ta), titanium (Ti), any other refractive metal,or an alloy thereof and may have a multilayer structure.

The active layer 121, the gate electrode 151, and the source and drainelectrodes 172 and 173 of the display device 1 may form a TFT T. Thegate electrode 151, which is the control terminal of the TFT T, may beconnected to the gate line, the source electrode 172, which is the inputterminal of the TFT T, may be connected to the data line, and the drainelectrode 173, which is the output terminal of the TFT T, may beelectrically connected to an anode electrode 191 via a contact hole 181.

The passivation layer 180 is disposed on the source and drain electrodes172 and 173. The passivation layer 180 may include silicon nitride,silicon oxide, silicon oxynitride, or an acrylic organic compound havinga low dielectric constant, benzocyclobutane (BCB), orperfluorocyclobutane (PFCB).

The passivation layer 180 may protect the source and drain electrodes172 and 173 and may also planarize the top surfaces of the source anddrain electrodes 172 and 173. The contact hole 181 may be formed topenetrate the passivation layer 180 and thus to expose the drainelectrode 173 therethrough.

The organic light-emitting element E is disposed on the passivationlayer 180. The organic light-emitting element E includes the anodeelectrode 191, a pixel-defining layer 190, an organic light-emittinglayer 192, and a cathode electrode 193.

The anode electrode 191 is disposed at a lowermost part of the organiclight-emitting element E. The anode electrode 191 may be electricallyconnected to the drain electrode 173 via the contact hole 181, which isformed in the passivation layer 180, and may function as a pixelelectrode of the organic light-emitting element E.

The anode electrode 191 may include a material layer having a high workfunction such as a layer of indium tin oxide (ITO), indium zinc oxide(IZO), zinc oxide (ZnO), or indium oxide (In₂O₃). The anode electrode191 may consist of a stack of the aforementioned material layer and areflective metal layer formed of lithium (Li), calcium (Ca), lithiumfluoride (LiF)/Al, Al, silver (Ag), magnesium (Mg), or gold (Au).

The pixel-defining layer 190 is disposed on the anode electrode 191. Thepixel-defining layer 190 may include a polyacrylate resin or a PI resin.The pixel-defining layer 190 may define each pixel of the organiclight-emitting element E and may include an opening 195, which exposesthe anode electrode 191.

The organic light-emitting layer 192 is disposed on a part of the anodeelectrode 191 exposed through the opening 195. The organiclight-emitting layer 192 may be formed as a multilayer including atleast one of a hole injection layer (HIL), a hole transport layer (HTL),an electron transport layer (ETL), and an electron injection layer(EIL).

The cathode electrode 193 is disposed on the pixel-defining layer 190and the organic light-emitting layer 192. The cathode electrode 193 mayinclude Li, Ca, LiF/Ca, LiF/Al, Al, Mg, Ag, platinum (Pt), palladium(Pd), nickel (Ni), Au-neodymium (Nd), iridium (Ir), Cr, barium fluoride(BaF), Ba, or a compound or mixture thereof (e.g. a mixture of Ag andMg). The cathode electrode 193 may function as a common electrode of theorganic light-emitting element E.

The encapsulation layer 194 is disposed on the cathode electrode 193.The encapsulation layer 194 may prevent moisture or air frominfiltrating into, and oxidizing, the organic light-emitting element Eand may planarize the top surface of the organic light-emitting elementE.

In exemplary embodiments, the display element unit 100 may furtherinclude a touch screen (not illustrated), which is attached to, orembedded in, the display element unit 100.

The adhesive layer 210 and the protective film 220 are disposed on thedisplay element unit 100. The adhesive layer 210 may be disposeddirectly on the encapsulation layer 194, which is located at anuppermost part of the display element unit 100.

The adhesive layer 210 attaches and fixes the protective film 220 ontothe display element unit 100. For example, the adhesive layer 210 mayinclude a pressure sensitive adhesive (PSA), but the exemplaryembodiments are not limited thereto.

The protective film 220, like the protective layer 10, protects thedisplay device 1 against foreign materials and physical impact.

The protective film 220 may be elastic and flexible enough to allow thedisplay device 1 to maintain its flexible characteristics. For example,the protective film 220 may be formed as a single layer or a multilayerincluding a material such as tempered glass, polyurethane (PU), PI,polyethylene terephthalate (PET), polycarbonate (PC), orpolymethylmethacrylate (PMMA), and the protective film 220 may furtherinclude at least one of a hard coating layer, an anti-finger (AF)coating layer, an anti-reflection (AR) coating layer, an anti-glare (AG)coating layer, and a polarizer. However, the exemplary embodiments arenot limited to this example.

The lowering of the neutral plane by the protective layer 10 willhereinafter be described with reference to FIGS. 3 and 4.

FIG. 3 is a cross-sectional view illustrating an arbitrary multilayerstack bent by external stress, and FIG. 4 is a cross-sectional viewillustrating neutral planes of display devices 1′ and 1.

Referring to FIG. 3, in a case in which a multilayer stack is bent inone direction by external force, a first layer TL, which is a part ofthe multilayer stack that stretches, receives tensile stress, and asecond layer CL, which is a part of the multilayer stack that contracts,receives compressive stress, and a neutral plane NP where the tensilestress and the compressive stress offset each other and thus become zeromay be formed between the first and second layers TL and CL. Thelocation of the neutral plane NP may vary depending on the rigidities ofthe first and second layers TL and CL and the overall thickness of themultilayer stack.

A flexible display device is generally bent in the same manner asillustrated in FIG. 3, and elements for realizing an image viewingfunction are generally robust against compressive stress, but may besusceptible to tensile strength.

Referring to FIG. 4, by additionally providing a protective layer 10,which has a given thickness (20 μm or thicker) and a given Young'smodulus (e.g. 20 Gpa or lower), at the bottom of a display device 1′,the location of the neutral plane NP may be lowered close to theprotective layer 10 and the flexible substrate 20. In FIG. 4, theneutral plane NP of the display device 1′ extends along the displayelement unit 100, but the neutral plane NP of the display device 1,which includes the protective layer 10 disposed on the bottom of theflexible substrate 20, extends along the flexible substrate 20. As aresult, most tensile stress acts only on the protective layer 10 and theflexible substrate 20, which are sufficiently elastic and flexible, andthus, elements above the neutral plane NP may only receive compressivestress and may be protected against tensile stress.

Other exemplary embodiments will hereinafter be described.

FIG. 5 is a cross-sectional view illustrating a stack structure of adisplay device according to another exemplary embodiment.

A display device 1_1 of FIG. 5 is the same as the display device 1 ofFIGS. 1 and 2 except that a protective layer 10_1 thereof includeslayers having different densities, and thus will hereinafter bedescribed, focusing mainly on the difference from the display device 1of FIGS. 1 and 2.

Referring to FIG. 5, the protective layer 10_1 may have a structure inwhich high-density layers 11 and low-density layers 12 having a lowerdensity than the high-density layers 11 are alternately stacked.

Since the density of the protective layer 10_1 may vary from one layerto another layer, the Young's modulus of the protective layer 10_1 mayalso vary from one layer to another layer. For example, the high-densitylayers 11 may have a high Young's modulus, and the low-density layers 12may have a lower Young's modulus than the high-density layers 11.

More than one high-density layer 11 and more than one low-density layer12 may be alternately stacked in the protective layer 10_1, and thelowermost and uppermost layers of the protective layer 10_1 may both behigh-density layers 11, may be a high-density layer 11 and a low-densitylayer 12, respectively, may be a low-density layer 12 and a high-densitylayer 11, respectively, and may both be low-density layers 12.

In the protective layer 10_1, a low-density layer 12 inserted betweenadjacent high-density layers 11 may be provided to increase the overallthickness of the protective layer 10_1 and maintain the overallelasticity or flexibility of the protective layer 10_1, and may thusfurther lower the neutral plane NP. The high-density layers 11 maystrengthen the functions of the protective layer 10_1, particularly, thefunction of preventing infiltration of moisture, air, or foreignmaterials.

FIGS. 6 through 8 are cross-sectional views illustrating stackstructures of display devices according to other exemplary embodiments.

Display devices 1_2, 1_3, and 1_4 of FIGS. 6, 7, and 8 are the same asthe display device 1 of FIGS. 1 and 2 except that the density ofprotective layers 10_2, 10_3, and 10_4 thereof gradually increase ordecrease along a vertical direction, and thus will hereinafter bedescribed, focusing mainly on the differences from the display device 1of FIGS. 1 and 2.

Referring to FIG. 6, the density of the protective layer 10_2 maygradually increase from the bottom to the top of the protective layer10_2. By controlling the density of the protective layer 10_2, asillustrated in FIG. 6, the thickness of the protective layer 10_2 may beincreased while maintaining the overall elasticity or flexibility of theprotective layer 10_2, and as a result, a neutral plane may beeffectively lowered.

Since the density of the protective layer 10_2 may vary from one part toanother part of the protective layer 10_2, the Young's modulus of theprotective layer 10_2 may also vary from one part to another part of theprotective layer 10_2. For example, the Young's modulus of theprotective layer 10_2 may gradually increase from the bottom to the topof the protective layer 10_2.

Referring to FIG. 7, the density of the protective layer 10_3 maygradually increase from the top to the bottom of the protective layer10_3. Referring to FIG. 8, the density of the protective layer 10_4 maygradually increase from the top or bottom to the middle of theprotective layer 10_4, or vice versa. As mentioned above, by controllingthe density of the protective layer 10_3 or 10_4, as illustrated in FIG.7 or 8, a neutral plane may be effectively lowered.

As mentioned above, the Young's modulus of the protective layer 10_3 or10_4 may also vary depending on the density of the protective layer 10_3or 10_4.

FIGS. 9 through 11 are cross-sectional views illustrating stackstructures of display devices according to still other exemplaryembodiments.

A display device 1_5 of FIG. 9 is the same as the display device 1 ofFIGS. 1 and 2 except that it does not include any flexible substrate 20,and thus will hereinafter be described, focusing mainly on thedifference with the display device 1 of FIGS. 1 and 2.

Referring to FIG. 9, in the display device 1_5, a protective layer 10may be disposed directly on a second surface of a display element unit100 without any flexible substrate 20 interposed between the protectivelayer 10 and the display element unit 100.

Since the protective layer 10 may have a given Young's modulus, WVTR,and CTE, the protective layer 10 not only protects the display device1_5, but also serves as a base substrate of a flexible display device,replacing the flexible substrate 20. In this case, the protective layer10 may have a thickness of 20 μm or thicker.

A display device 1_6 of FIG. 10 is the same as the display device 1_5 ofFIG. 9 except that a protective layer 10_1 thereof includes layershaving different densities.

A display device 1_7 of FIG. 11 is the same as the display device 1_6 ofFIG. 10 except that a protective film 21 is further provided on a secondsurface of a protective layer 10_1 and is attached on the protectivelayer 10_1 by an adhesive layer 2.

The adhesive layer 2 and the protective film 21 at the second surface ofthe protective layer 10_1 may include the same materials or the samelayers as an adhesive layer 210 and a protective film 220 on a firstsurface of a display element unit 100.

FIGS. 12 through 16 are cross-sectional views illustrating amanufacturing method of a display device, according to an exemplaryembodiment.

Referring to FIG. 12, a flexible substrate 20 is formed on a sacrificialsubstrate 13, which is formed of a material with high rigidity such asglass. The sacrificial substrate 13 may serve as a supporting substrateduring the formation of a TFT or an organic light-emitting element andmay be separated and removed after the formation of such element. Tofacilitate the separation of the sacrificial substrate 13, a sacrificiallayer (not illustrated) may be formed between the sacrificial substrate13 and the flexible substrate 20.

During the fabrication of a display device having no flexible substrate20, such as the display device 1_5 of FIG. 9, the formation of theflexible substrate 20 may not be performed, in which case, a bufferlayer 110 may be formed directly on the sacrificial substrate 13.

Referring to FIG. 13, a display element unit 100 including a TFT T andan organic light-emitting element E is formed on a first surface of theflexible substrate 20. The first surface of the flexible substrate 20 isopposite to a second surface of the flexible substrate 20 which iscloser to the sacrificial substrate 13.

Referring to FIG. 14, the sacrificial substrate 13 is separated from theflexible substrate 20. For example, the sacrificial substrate 13 may bedetached from the flexible substrate 20 by applying light such as laserlight or physical force to the sacrificial substrate 13, but theexemplary embodiments are not limited thereto. In a case in which thesacrificial layer is formed between the sacrificial substrate 13 and theflexible substrate 20, the sacrificial substrate 13 may be separatedfrom the flexible substrate 20 by applying laser light to thesacrificial layer.

Referring to FIG. 15, a protective layer 10 is formed by depositing anorganic material on the second surface of the flexible substrate 20. Thedeposition of the organic material may be performed at a low temperatureof, for example, 90° C. or lower. If the deposition of the organicmaterial is performed at low temperature, various elements or layersalready formed in the display element unit 100 may be prevented frombeing damaged during the deposition of the organic material. Also, thedegree of freedom in selecting materials for various elements or layersof the display element unit 100 may be increased.

A material that can be deposited at a low temperature of about 90° C.may be selected as the organic material. For example, the organicmaterial may include at least one of parylene (i.e., a poly(p-xylylene)polymer) and a derivative thereof, which may be represented by Formula1:

where n is a natural number equal to or greater than 2, m is an integernumber between 0 and 4, X is hydrogen or halogen, and R is halogen oralkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl,or a halide thereof having 1 to 8 carbon atoms.

The material represented by Formula 1 include at least one of materialsrepresented by Formulas 2 through 5:

where n is a natural number equal to or greater than 2.

In a case in which the protective layer 10 is formed using parylene-N,which is the material of Formula 2, a parylene-N monomer layer may beformed by introducing and polymerizing a parylene-N monomer, startingfrom locations on the flexible substrate 20 where temperature is low.Parylene-N may be a low-temperature deposition material that can bedeposited at a temperature of as low as about −40° C.

In a case in which the protective layer 10 is formed using parylene-F,which is the material of Formula 5, a parylene-F layer may be formed byintroducing and polymerizing a parylene-F dimer, starting from thelocations on the flexible substrate 20 where temperature is low.Parylene-F may be a low-temperature deposition material that can bedeposited at room temperature.

As mentioned above, since the protective layer 10 may be formed bydepositing the organic material at low temperature without theirradiation of light, the use of an additional adhesive is unnecessary,and the elements in the display device 1 may be prevented from beingdamaged by light or heat.

By changing the conditions for the deposition of the organic materialover time, the concentration of the organic material, i.e., the densityof the protective layer 10, may be controlled in the same manner as thatillustrated in any one of FIGS. 5 through 8. A structure in which thedensity of the protective layer 10 varies from one part to another partof the protective layer 10 has already been described above, and thus, adetailed description thereof will be omitted. As mentioned above, sincethe density of the protective layer 10 may vary from one part to anotherpart, the Young's modulus of the protective layer 10 may also vary fromone part to another part.

Referring to FIG. 16, a protective film 220 is attached on the displayelement unit 100. The protective film 220 may be attached and fixed onthe display element unit 100 via the adhesive layer 210, which includesan adhesive.

FIGS. 12 through 16 illustrate an example in which the attachment of theprotective film 220 is performed after the separation of the sacrificialsubstrate 13 and the formation of the protective layer 10, but theexemplary embodiments are not limited thereto. For example, theseparation of the sacrificial substrate 13 and the formation of theprotective layer 10 may be performed after the attachment of theprotective film 220 on the display element unit 100. For anotherexample, the attachment of the protective film 220 on the displayelement unit 100 may be performed after the separation of thesacrificial substrate 13 before the formation of the protective layer10.

Experimental examples showing that the impact resistance of a displaydevice can be strengthened by lowering a neutral plane with the use of aprotective layer will hereinafter be described.

Manufacturing Example

A display device in which an urethane cushion layer having a thicknessof 150 μm, a first PSA layer having a thickness of 30 μm, a PI layerhaving a thickness of 38 μm, a second PSA layer having a thickness of 25μm, a parylene-F layer having a thickness of 10 μm, a display elementunit including a TFT and an organic light-emitting element, a third PSAlayer having a thickness of 35 μm, a PI layer having a thickness of 50μm, and a PU layer having a thickness of 200 μm were sequentiallystacked was fabricated. The parylene-F layer was formed according to themethod described above with reference to FIGS. 12 through 16.

Comparative Example

A display device according to a comparative example was fabricated inthe same manner as the display device according to the manufacturingexample except that the parylene-F layer was not provided and thedisplay element unit was directly stacked on the second PSA layer.

Experimental Example

The display device according to the manufacturing example and thedisplay device according to the comparative example were evaluated fortheir impact resistances by dropping each of a 5.8 g Bic Ball a 5.5 gsteel pen thereover.

More specifically, the dropping heights of the Bic Ball and the steelpen that produced contrast points for the first time in each of thedisplay device according to the manufacturing example and the displaydevice according to the comparative example were measured, and theresults are as shown in Table 1 below.

TABLE 1 Manufacturing Example Comparative Example 5.8 g Bic Ball 8 cm 6cm 5.5 g Steel Pen 7 cm 4 cm

In response to the Bic Ball or the steel pen colliding with each of thedisplay device according to the manufacturing example and the displaydevice according to the comparative example, the bottom surfaces of thedisplay device according to the manufacturing example and the displaydevice according to the comparative example both stretched, and the topsurfaces of the display device according to the manufacturing exampleand the display device according to the comparative example bothcontracted. However, as is apparent from Table 1, display elements inthe display device according to the manufacturing example that are abovea neutral plane were less affected by tensile stress because a parylenelayer was further provided to lower the neutral plane.

Although certain exemplary embodiments and implementations have beendescribed herein, other embodiments and modifications will be apparentfrom this description. Accordingly, the inventive concept is not limitedto such embodiments, but rather to the broader scope of the presentedclaims and various obvious modifications and equivalent arrangements.

What is claimed is:
 1. A manufacturing method of a display device,comprising: forming a flexible substrate on a sacrificial substrate;forming a display element unit on a first surface of the flexiblesubstrate, the display element unit comprising a TFT and an organiclight-emitting element; separating the sacrificial substrate from theflexible substrate; and forming a protective layer by depositing anorganic material on a second surface of the flexible substrate, thesecond surface being opposite to the first surface, wherein theprotective layer has a structure in which more than one first layer andmore than one second layer having a lower density than the first layerare alternately stacked.
 2. The manufacturing method of claim 1, whereinthe organic material is deposited at a temperature of 90° C. or lower.3. The manufacturing method of claim 1, wherein the protective layercomprises at least one material of Formula 1:

where n is a natural number equal to or greater than 2, m is an integernumber between 0 and 4, X is hydrogen or halogen, and R is halogen oralkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl,or a halide thereof having 1 to 8 carbon atoms.
 4. The manufacturingmethod of claim 1, wherein a combined thickness of the protective layerand the flexible substrate is 20 μm or greater.
 5. The manufacturingmethod of claim 1, wherein a Young's modulus of the protective layer is20 GPa or lower.
 6. A manufacturing method of a display device,comprising: forming a flexible substrate on a sacrificial substrate;forming a display element unit on a first surface of the flexiblesubstrate, the display element unit comprising a TFT and an organiclight-emitting element; separating the sacrificial substrate from theflexible substrate; and forming a protective layer by depositing anorganic material on a second surface of the flexible substrate, thesecond surface being opposite to the first surface, wherein the formingthe protective layer comprises changing conditions for the deposition ofthe organic material over time such that a protective layer comprisestwo or more layers having different densities or Young's moduli.